Study of the stress-strain and temperature fields in cutting tools using laser interferometry

OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. No. 4 2021 lens (11) of the camera (12). A collimated backlight was used (13) to determine the tool and workpiece contours. A strain gauge multicomponent dynamometer (14) with an ampli fi er (15) and an analog-to-digital converter (16) were used to record the force components during the cutting process. Interference fringes and the acting cutting forces were recorded in the computer memory (17). The use of a polarized beam splitter cube and a quarter-wave plate made it possible to minimize the ghost re fl ections of the laser beam, which practically eliminated the moiré effect and signi fi cantly reduced the loss of luminous fl ux. It improved the image quality of the recorded interference patterns, which is necessary for high-speed recording with brief exposure. The experimental setup was mounted on a retro fi tted lathe model 163 (Fig. 2). A thyristor drive KEMTOK with a DC motor was used to rotate the spindle, which provided a stepless adjustment of the cutting speed. On the cross slide of the machine, the UDM-600 dynamometer (1) with a tool holder, two single-channel RDP 628 strain gauge ampli fi ers (2), and two aluminum pro fi le rails were fi xed on a base plate. A single-mode single-frequency DPSS laser LCM-S-111 (3) with a wavelength of 532 nm, a beam expander (4), adjustable holders with a beam splitter (5), and a zero-order wave plate (6) were installed on one guide. A high-speed digital video camera Fastec HiSpec 2-HR (7) with a NAVITAR Zoom 6000 lens (8) was fi xed on the second rail. The optical wedge (9) was mounted on a tool holder in an adjustable frame. All optical elements had antire fl ective coatings, and the tool holder design was optimized to improve the dynamic characteristics of the dynamometer. In the current version, the developed methods are applicable only for dry cutting without the use of cutting fl uids. The interference patterns obtained during the experiment include information about changes in  t c of the cutting tool width t c : 1 , c t m n   = (1) where n is the refractive index of air ( n = 1 can be taken with suf fi cient accuracy), m is the number of in- terference fringes that have moved relative to the point of interest (the interference fringe order), and  is the wavelength (for the used laser  = 532 nm). At the same time, the lateral strains can be found as follows: . c z c t t   = (2) Substituting (2) into (1), we obtain: . z c m t   = (3) To determine the difference in the interference fringe orders m , two interference patterns need to be analyzed – the pattern before the application of load and after loading; using these patterns in the section of interest (for example, along the tool faces of the cutting tool), the fringe order distributions ( m 1 and m 2 , respectively) can be found. By subtracting the obtained plots, the total deformation (thermal and forces acting) plot m s = ( m 2 − m 1 ) was obtained. To obtain a plot of only deformations by forces acting on m p , the plot of thermal deformations m t is subtracted from the m s plot: m p = m s – m t . The plot of thermal deformations m t can be obtained from the interference pattern recorded immediately after the rapid interruption of the cutting process. Fig. 2. View of the experimental rig based on a lathe